1. Field of the Invention
The present invention relates to solid waste treatment agents and a method of treating solid waste, by which harmful metals and organic chlorinated compounds such as dioxins and polychlorinated biphenyl (PCB) contained in solid waste such as incineration ash, smoke dust, slag, sludge, soil or shredder dust can be made harmless to facilitate handling in subsequent treatment steps of the solid waste.
2. Description of the Background Art
Various metal elements are contained in solid waste such as smoke dust generated in a refuse incineration ground, sludge exhausted from a mine, activated sludge used in a waste water treatment or contaminated soil, and heavy metal elements, such as mercury, cadmium, zinc, copper and chromium, harmful to the human body may be contained in plenty in many cases. When these metals are dissolved out of the solid waste, there is a possibility that underground water, rivers, seawater and the like may be contaminated.
Therefore, there has heretofore been adopted a treatment method in which solid waste is cemented and then buried in the ground. However, this method has a possibility that metals may be dissolved out in seawater or rainwater through a cement wall when the cemented solid waste comes into contact with the seawater or rainwater, and has hence not been always said to be a safe treatment method. A treatment method in which a metal scavenger is added to solid waste to immobilize metals, and the solid waste is then bound with cement or the like is also performed.
However, the method of immobilizing the metals in the solid waste by the metal scavenger has involved a problem that the reactivity of the metal scavenger to the metals in the solid waste is not always sufficient due to the low penetrating power of the metal scavenger into the solid waste, so that the metals contained in the solid waste may not be sufficiently immobilized in some cases. In addition, since the metal scavenger is difficult to immobilize calcium contained in the solid waste, and calcium not immobilized is easy to be dissolved out in water from the solid waste, there is a possibility that even when the solid waste treated with the metal scavenger is further bound with cement or the like to finally dispose it, unimmobilized calcium in the solid waste and calcium in the cement wall may be easy to be dissolved out when exposed to rain or the like, and not only the cement wall may become easy to be broken down as the calcium is dissolved out, but also other metals immobilized by the metal scavenger in the solid waste may become easy to be isolated. Further, it has heretofore been necessary to bind the solid waste with a great amount of cement or the like to treat it, which offers a problem to subsequent treatments and transfer, because the volume of the solid waste after bound with the cement or the like becomes larger than the treatment needs.
In recent years, the generation of dioxins upon refuse incineration has become a major social problem, and there is also a possibility that organic chlorinated compounds such as dioxins may be contained in smoke dust formed by refuse incineration. However, it has been difficult to make the organic chlorinated compounds such as dioxins in the smoke dust harmless by the conventional treatment methods. Further, in recent years, PCB widely used as a heat transfer medium or the like has not been used because it is harmful to the human body. However, soil and the like may possibly be contaminated with PCB discarded in some cases. It has however been said to be difficult to treat the soil and the like contaminated with PCB, since PCB is a thermally and chemically very stable compound.
In order to treat the organic chlorinated compounds such as dioxins, there has heretofore been adopted a method of treating them at a high temperature of at least 600.degree. C. or a method of heat-treating them at 400.degree. C. or higher in an atmosphere containing a low concentration of oxygen. However, these methods have involved a problem that a treating apparatus having excellent heat resistance or a special treating apparatus capable of keeping the atmosphere at a low oxygen concentration is required, and so plant and equipment investment is expensive.